JP2000268857A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the charge/discharge characteristics of a battery by forming a positive electrode from lithium-manganeze oxide having a spinel structure, forming a negative electrode from a carbon material, and designing a specific organic electrolytic solution. SOLUTION: This lithium ion secondary battery includes a positive electrode consisting of lithium-manganese oxide having spinel structure, a negative electrode consisting of a carbon material where lithium ions are inserted and separated, and an organic electrolytic solution. The organic electrolytic solution is formed by dissolving lithium salt in a mixture solvent containing cyclic carbonate and chain carbonate, in which at least one of butane sulfon and butadiene sulfon is included in 0.5-10 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery in which an organic electrolyte is improved to improve a charge and discharge cycle.

In recent years, the spread of electric vehicles has been called out due to environmental problems such as air pollution. Along with this, there is a demand for higher performance of batteries as power sources. Conventionally, a lithium ion secondary battery composed of a positive electrode made of a lithium transition metal composite oxide, a negative electrode made of a carbon material, and an organic electrolyte has been known as one of high-performance batteries, and features a high energy density. There is.

[0003] Lithium ion secondary batteries have already been put to practical use in portable electronic devices and the like. However, this conventional lithium secondary battery uses a layered lithium-cobalt oxide as a positive electrode, and has a problem that the cost of the cobalt constituting the lithium-cobalt oxide is high and the resources are small.

On the other hand, since it is important for an electric vehicle to construct a battery using a low-cost and resource-rich substance, lithium manganese oxide having a spinel structure has attracted attention instead of layered lithium cobalt oxide. ing. However, it is known that the lithium-ion secondary battery using lithium manganese oxide for the positive electrode has a remarkable decrease in battery capacity with repeated charge / discharge compared to the lithium-ion secondary battery using lithium cobalt oxide. Improvement of the charge / discharge cycle characteristics is indispensable.

[0005]

One of the causes of a decrease in battery capacity due to a charge / discharge cycle is that lithium ions that can be discharged by the reaction of a negative electrode charged with lithium ions and a solvent in an electrolyte solution. Is said to be partially deactivated.

[0006] The electrolyte solvent widely used at present is a composite system of a cyclic carbonate having a high dielectric constant, mainly ethylene carbonate, and a low-viscosity chain carbonate such as diethyl carbonate or dimethyl carbonate.
However, even in these electrolyte systems, they gradually react with the charged negative electrode. In addition, since the deactivated lithium ions are present on the surface of the negative electrode active material as a film of a lithium compound having a large electric resistance, they prevent other lithium ions from entering and exiting, and promote a decrease in capacity due to charge and discharge.

In view of such circumstances, a method for forming a film having good lithium ion permeability has been proposed, and among them, a film containing a sulfur atom is said to be good. Japanese Patent Application Laid-Open No. 9-320596 proposes that the surface of a negative electrode is previously coated with a sintered body of an organic substance containing sulfur. The coating is considered to have good lithium ion permeability, and it is said that the battery capacity does not decrease much during charging and discharging. However, there is a problem in that it is difficult to cover the negative electrode surface uniformly with the fired product in terms of synthesis.

On the other hand, many proposals have been made to decompose a specific solvent on the surface of the negative electrode during charging to form a film having high lithium ion permeability on the surface of the negative electrode. For example, Japanese Patent Application Laid-Open No. Hei 10-189041 proposes a battery having an electrolyte containing 0.1 to 50% by weight of alkanesulfonic anhydride.

Japanese Patent Application Laid-Open No. 10-189042 discusses the inclusion of a cyclic sulfate in an electrolytic solution. However, although examples of applying these compounds to lithium ion secondary batteries composed of natural graphite and metallic lithium have been shown, their application to batteries using lithium manganese spinel has not been clarified.

With respect to butane sultone, which will be described further below,
JP-A-10-55822 proposes a lithium cobalt oxide / silver-supported natural graphite battery using an electrolyte containing 10 to 50% by weight of butane sultone. This relates to the flame retardancy of the battery, and does not show any charge / discharge characteristics.

JP-A-10-50342 reports an example in which an electrolyte comprising propane sultone or butane sultone and a chain carbonate such as diethyl carbonate is applied to a lithium cobalt oxide / pitch coke fired battery. I have. When the electrolytic solution in this case was used as it was in a battery composed of lithium manganese spinel and graphite, it became clear that the charge / discharge efficiency was extremely poor as described later.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In a lithium ion secondary battery having a lithium manganese oxide having a spinel structure as a positive electrode and a carbon material as a negative electrode, a specific organic electrolyte is provided. Is designed to improve the charge / discharge characteristics of the battery.

[0013]

The present invention relates to a lithium ion secondary battery having a positive electrode made of lithium manganese oxide having a spinel structure, a negative electrode made of a carbon material into and out of which lithium ions are inserted and an organic electrolyte. The organic electrolyte is obtained by dissolving a lithium salt in a mixed solvent containing a cyclic carbonate and a chain carbonate,
A lithium ion secondary battery comprising at least one of butane sultone and butadiene sulfone in a volume ratio of 0.5 to 10%.

The most remarkable feature of the present invention is that it contains both cyclic carbonate and chain carbonate and at least one of butane sultone or butadiene sulfone in a volume ratio of 0.5 to 10%. That is.

[0015] Butane sultone and butadiene sulfone are both cyclic sulfur compounds and are very effective in improving the charge / discharge characteristics. Therefore, the same effect may be obtained by other cyclic sulfur compounds. However, at present, the above-mentioned butane sultone and butadiene sulfone have been found to be excellent in the effect of improving the charge / discharge characteristics.

Either one of butane sultone and butadiene sulfone may be contained in an organic solvent, or both may be mixed and contained. In any case, the content is 0.5 to 10% (vol%) of the total solvent amount. If the content is less than 0.5%, there is a problem that the formation of a film having good permeability is insufficient, and the degree of improvement of the charge / discharge characteristics is small. On the other hand, if it exceeds 10%, there is a problem that the decomposition of the solvent at the time of charging becomes large and the charge / discharge characteristics are rather deteriorated.

As described above, a mixed solvent containing a cyclic carbonate and a chain carbonate is used as the organic solvent of 95 to 99.5% other than the above-mentioned butane sultone and butadiene sulfone. When a solvent containing only one of the cyclic carbonate and the chain carbonate is used, the effect of the case containing butane sultone or butadiene sulfone cannot be sufficiently obtained. The mixed solvent may be mixed with other solvents in addition to the cyclic carbonate and the chain carbonate.

As the above cyclic carbonate, for example,
Examples include ethylene carbonate (ethylene carbonate), propylene carbonate, and butylene carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and dipropyl carbonate.

Examples of those which can be contained in addition to these cyclic carbonates and chain carbonates include lactones such as γ-butyrolactone, γ-hexanolactone, valerolactone and ε-caprolactone. As the lithium salt, LiP
F ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN
(CF ₃ SO ₂ ) ₂ and the like.

As the positive electrode, a known lithium manganese oxide having a spinel structure can be used. That is, a known lithium manganese spinel, a lithium excess lithium manganese spinel,
Lithium manganese spinel substituted with a dissimilar metal such as i, Al, Co, Fe, and Mg, and a mixture thereof can be used.

The negative electrode is made of a carbon material into which lithium ions are inserted and desorbed. That is, for example, known natural graphite, artificial graphite, cokes, and carbons obtained by calcining raw coke can be used.

Next, the operation of the present invention will be described. In the present invention, the organic electrolyte contains both cyclic carbonate and chain carbonate,
The specific cyclic sulfur compound is contained in the specific amount. As a result, the charge / discharge characteristics are significantly improved as compared with the conventional case. It is considered that the reason for this is that the above-mentioned cyclic sulfur compound is decomposed on the surface of the negative electrode at the time of charging to form a good film that makes lithium ions enter and exit quickly.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A lithium ion secondary battery according to an embodiment of the present invention will be described using seven examples (E11 to E17 and five comparative examples (C11 to C15)). The lithium ion secondary battery in this example is a lithium ion secondary battery having a positive electrode made of lithium manganese oxide having a spinel structure, a negative electrode made of a carbon material into which lithium ions are inserted and desorbed, and an organic electrolyte. is there.

The above-mentioned organic electrolyte solution in Examples E11 to E17 is obtained by dissolving a lithium salt in a mixed solvent containing cyclic carbonate and chain carbonate, and containing 0.5 to 10% by volume of butane sultone. are doing. On the other hand, in Comparative Examples C11 to C15, the content of butane sultone was adjusted to be outside the above range. In this example, in particular, the appropriate value of the butane sultone content was confirmed by measuring the initial discharge capacity. Hereinafter, the manufacturing methods of Examples E11 to E17 and Comparative Examples C11 to C15 will be described first.

First, for the positive electrode, 90 _% lithium manganese spinel Li _1.15 Mn _1.85 O ₄ (manufactured by Honjo Chemical) was used.
Parts by weight, 7 parts by weight of carbon black TB5500 (manufactured by Tokai Carbon), 7 parts by weight of polyvinylidene fluoride PVDF (Kureha Chemical), and N-methylpyrrolidone (NM)
P) to prepare a slurry. The slurry is applied on an aluminum foil, pressed, and then dried to a diameter of 15 mm.
Punched into a disk. As a result, the thickness of the electrode material becomes 53
A positive electrode of μm was obtained.

Next, for the negative electrode, spherical artificial graphite MCM was used.
A slurry was prepared by mixing 95 parts by weight of B2528 (Osaka Gas Chemical) and 5 parts by weight of the above PVDF with NMP. The slurry was applied to a copper foil, pressed, dried, and punched into a disk having a diameter of 17 mm. Thus, a negative electrode having a thickness of the electrode material of 40 μm was obtained. Next, using the positive electrode and the negative electrode, a polyethylene separator (manufactured by Tonen Chemical Co., Ltd.), and an organic electrolyte prepared as follows, a coin battery having a battery capacity of about 2 mAh (Example E)
11 to E17 and Comparative Examples C11 to C15).

As the organic electrolyte, LiPF ₆ (manufactured by Toyama Pharmaceutical Co., Ltd.) as a lithium salt, ethylene carbonate (EC) as a cyclic carbonate, diethyl carbonate (DEC) as a chain carbonate, and butane sultone (B
S; Tokyo Chemical Industry Co., Ltd.). Then, the concentration of LiPF ₆ was adjusted to 1 mol / liter, and EC was 33% of the total volume of the solvent. Remaining solvent 67% is DEC and BS
And the content of BS, as shown in Table 1,
This was changed for each sample.

Next, each of the obtained coin batteries was stored at a temperature of 25.
At ℃, the battery was charged to 4.2 V at a constant current of 1.0 mA / cm ² and further charged at a constant voltage of 4.2 V until the total charging time was 4 hours. Thereafter, after a pause of 10 minutes, the discharge was continued to 3.0 V at a constant current of 0.5 mA / cm ² (hereinafter, this charge / discharge is referred to as a cycle test). This operation was repeated to measure the cycle characteristics of the battery. Table 1 summarizes the discharge capacity per positive electrode active material in the first charge / discharge cycle (first time).

[0029]

[Table 1]

As can be seen from Table 1, Examples E11 to E17 in which the content of BS is 0.5 to 10.0%.
It can be seen that all have larger discharge capacities than Comparative Examples C11 to C15. From this, it is understood that the content of butane sultone (BS) is preferably 0.5 to 10.0%, more preferably 1.0 to 5.0%.

Embodiment 2 In this embodiment, the butane sultone (B
Butadiene sulfone (manufactured by Aldrich) was added to the organic electrolyte in place of S). The appropriate value of the butadiene sulfone content was confirmed by measuring the initial discharge capacity. Table 2 shows the content of butadiene sulfone in the organic electrolyte. The other conditions are the same as those of the first embodiment, and five examples (E21 to E25) according to the present invention are provided.
And four lithium ion secondary batteries of Comparative Examples (C21 to C24).

Next, a cycle test was performed in the same manner as in the first embodiment. As can be seen from Table 2, Examples E21 to E25 in which the content of butadiene sulfone is 0.5 to 10.0% have a larger discharge capacity than Comparative Examples C21 to C24. From this, it is understood that the content of butadiene sulfone is optimally 0.5 to 10.0%.

[0033]

[Table 2]

Embodiment 3 In this embodiment, the effect of improving the charge-discharge cycle characteristics by adding butane sultone or butadiene sulfone to the organic electrolyte was confirmed. As samples, two examples E31 and E32 of the present invention and one comparative example C31 were used. First, a method for manufacturing a lithium ion secondary battery according to Examples E31 and E32 and Comparative Example C31 will be described.

First, for the positive electrode, 86 _{g of} lithium manganese spinel Li _1.10 Mn _1.90 O ₄ (manufactured by Honjo Chemical) was used.
Parts by weight, 10 parts by weight of artificial graphite (Rosan), and 4 parts by weight of polyvinylidene fluoride PVDF (Kureha Chemical)
The mixture was mixed with N-methylpyrrolidone (NMP) to prepare a paste. The paste was applied to both sides of an aluminum foil having a thickness of 20 μm, and then pressed and dried to obtain a positive electrode sheet having a thickness of 130 μm.

Next, for the negative electrode, spherical artificial graphite MCM was used.
A paste was prepared by mixing 94 parts by weight of B2528 (Osaka Gas Chemical) and 6 parts by weight of the above PVDF with NMP. This paste was applied on both sides of a copper foil having a thickness of 15 μm, and then pressed and dried to obtain a negative electrode sheet having a thickness of 82 μm.

Next, a polyethylene separator was sandwiched between the positive electrode sheet and the negative electrode sheet, and these were wound into a cylindrical shape to produce a 18650 type battery. And
Inject the organic electrolyte prepared as follows into this battery,
The lithium ion secondary batteries of Examples E31 and E32 and Comparative Example C31 were obtained.

The organic electrolyte solutions of Examples E31 and E32 were as follows:
Mol / liter of LiPF ₆ is a lithium salt, 30% of the total solvent of the organic electrolyte is EC, and the remaining 70% is B
Allocated by S and DEC. Example E31 contains 2% butane sultone (BS), and Example E32 contains 10% BS. The organic electrolytic solution of Comparative Example C31 was a 1 mol / liter LiPF ₆ / EC + electrolytic solution for batteries manufactured by Toyama Pharmaceutical.
DEC (volume mixing ratio 3: 7) was used.

Next, each battery was charged at a temperature of 25 ° C. with a constant current of 1.0 mA / cm ² to 4.2 V, and further charged at a constant voltage of 4.2 V for a total of charging time. For 3 hours. Thereafter, discharging was continued to 3.0 V at a constant current of 0.5 mA / cm ² . The charging and discharging operations were repeated five times to age the battery. Subsequently, after this aging, a temperature of 6
It was left in a thermostat at 0 ° C., and charge / discharge of a constant current method was repeated at a current density of 1.0 mA / cm ² between 3.0 V and 4.2 V to examine cycle characteristics.

FIG. 1 shows the results of this test. The figure shows
The horizontal axis shows the number of charge / discharge cycles after aging, and the vertical axis shows the discharge capacity (mAh / g) per positive electrode active material. As can be seen from the figure, Examples E31 and E32 each containing butane sultone in the organic electrolyte solution exhibited a higher discharge capacity in all measurement regions than Comparative Example C31 containing no butane sultone. From this, the addition of butane sultone to the organic electrolyte is
It turns out that it is effective in improving the cycle characteristics. Also,
From the comparison between Embodiment Examples E31 and E32, it is also understood that the addition amount of butane sultone is more effective at 2% than at 0.5%.

Embodiment 4 This embodiment is based on Embodiment E15 of Embodiment 1 in which 5% butane sultone is contained in the organic electrolyte solution.
Batteries using other cyclic sulfur compounds instead of the butane sultone (Comparative Examples C41 to C44) were produced. And
The difference in battery characteristics depending on the type of cyclic sulfur compound was confirmed.

Further, a battery was prepared without adding cyclic carbonate as a solvent in the organic electrolyte solution.
45), and the battery characteristics were measured. This comparative example C45
Is to investigate whether the organic electrolyte disclosed in Japanese Patent Application Laid-Open No. 10-50342, which is a conventional technique, can be directly applied to a battery having lithium manganese spinel and graphite as active materials.

The cyclic sulfur compounds other than butane sultone in Comparative Examples C41 to C44 are, as shown in Table 3, propane sultone (C41) and sulfolane (C
42), methylsulfolane (C43) and dipropyl sulfite (C44). The amounts of these additives were all 5% of the total amount of the solvent, and were the same as in Example E15. Others are the same as Example E15.

In the battery of Comparative Example C45, a mixture of butane sultone and diethyl carbonate (chain carbonate) at a mixing ratio of 1: 1 was used as a solvent for the organic electrolyte. And ethylene carbonate as a cyclic carbonate was not added. Others were the same as Example E15.

Each of these batteries (E15, C41 to C45)
The cycle test described in the first embodiment was performed on the test pieces. Table 3 shows the discharge capacity per positive electrode active material in the first cycle (first time) of the charge / discharge cycle.

As can be seen from Table 3, from the comparison between Example E15 and Comparative Examples C41 to C44, among the cyclic sulfur compounds, butane sultone, in particular, has a large discharge capacity and is effective in improving the charge / discharge cycle characteristics. . Also,
Examples E11 to 17 (Table 1) and Comparative Example C4 shown in Table 1
From the comparison of Table 5 (Table 3), when neither the cyclic carbonate nor the chain carbonate is contained as the organic electrolyte,
It can be seen that charge / discharge cycle characteristics cannot be improved.

[0047]

[Table 3]

[0048]

As described above, according to the present invention, in a lithium ion secondary battery having a lithium manganese oxide having a spinel structure as a positive electrode and a carbon material as a negative electrode,
By designing the specific organic electrolyte, the charge / discharge characteristics of the battery can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing charge / discharge cycle characteristics in a third embodiment.

Claims (1)

[Claims] 1. A lithium ion secondary battery comprising: a positive electrode made of lithium manganese oxide having a spinel structure; a negative electrode made of a carbon material into which lithium ions are inserted and desorbed; and an organic electrolyte. Is characterized in that a lithium salt is dissolved in a mixed solvent containing a cyclic carbonate and a chain carbonate, and that at least one of butane sultone or butadiene sulfone is contained in a volume ratio of 0.5 to 10%. Ion secondary battery.